This application claims the priority of Korean Patent Application No. 2002-87941, filed on Dec. 31, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission device, and more particularly, to a field emission device having a grid for electron control.
2. Description of the Related Art
In general, a triode field emission device composed of a cathode electrode, a gate electrode, and an anode electrode has a structure in which electrons are extracted by one gate electrode from a cathode and are simply accelerated toward the anode electrode. Thus, some electron beams properly not being controlled in this process and emitted, and may diverge and thus be collided with a phosphor deviating from a given pixel. Due to the improperly diverged emitted electron beams, color purity is lowered. Also, a high resolution display cannot be embodied with these uncontrolled electron beams. Also, the triode field emission device has another problem in that arcing easily occurs in the triode field emission device for some well-known reasons.
The most part of these problems is solved by a separate grid electrode where electrons can be controlled, and thus, a tetrode field emission device having the grid electrode is preferred. The grid electrode in the tetrode field emission device is disposed between an anode electrode and a gate electrode.
U.S. Pat. Nos. 5,710,483 and 6,373,176 disclose a field emission device with a tetrode structure having a grid electrode for electron control.
In a field emission device disclosed in U.S. Pat. No. 5,710,483, a grid electrode is provided by a deposited metallic material formed inside of a cathode plate on which a gate electrode is formed. And a grid electrode of a field emission device disclosed in U.S. Pat. No. 6,373,176 is formed by a metallic sheet which is separated from a cathode plate, and an anode plate and the cathode plate are isolated from each other by a spacer placed therebetween.
The grid electrode formed by depositing a metallic material is limited by the size of deposition equipment. This limitation in the size of deposition equipment causes to limit the maximum size of the field emission device which can be obtained, and thus, it is not proper to manufacture a large-sized field emission device. Thus, an apparatus for deposing a metallic layer required to manufacture a large-sized field emission device must to be newly designed and manufactured, but vast costs are required. Meanwhile, the thickness of the grid electrode formed by the deposited metallic layer is limited to maximum 2 microns, and thus is not enough to effectively control electron beams.
The size of the grid electrode formed by the metallic sheet is not limited, and thus is suitable for a large-sized field emission device. In particular, the thickness of the grid electrode can be freely selected, and electron beams can be effectively controlled. However, the grid electrode formed by the metallic sheet has the disadvantage that the grid electrode may be thermally deformed during a firing process of a phosphor layer and a binder for fixing a spacer while a field emission device is manufactured.
For understanding of the thermal deformation problem, a conventional tetrode field emission device will be briefly described with the drawings.
FIG. 1A is a cross-sectional view schematically illustrating an example of a conventional field emission device adopting a grid electrode (hereinafter, referred to as a mesh grid) with a mesh structure. Referring to FIG. 1A, a cathode plate 10 and an anode plate 20 are spaced apart from each other by a spacer 30. A space between the cathode plate 10 and the anode plate 20 is vacuumized. Thus, due to an internal negative pressure, the cathode plate 10 and the anode plate 20 are securely coupled to each other in the state that the spacer 30 is placed therebetween.
On the cathode plate 10, a cathode electrode 12 is formed on a rear plate 11, and a gate insulating layer 13 is formed on the cathode electrode 12. A through hole 13a is formed in the gate insulating layer 13, and the cathode electrode 12 is exposed to the bottom of the through hole 13a. An electron emission source 14 such as carbon nanotube (CNT) is formed on the cathode electrode 12 exposed through the through hole 13a. A gate electrode 15 having a gate hole 15a corresponding to the through hole 13a is formed on the gate insulating layer 13.
Meanwhile, on the anode plate 20, an anode electrode 22 is formed inside of a front plate 21, a phosphor layer 23 on the anode electrode 22 is formed opposite to the gate hole 15a, and a black matrix 24 is formed in the other portion of the anode electrode 22.
A mesh grid 40 is interposed between the cathode plate 10 and the anode plate 20 having the above structure. The mesh grid 40 is supported by the spacer 30 in a state when the mesh grid 40 is spaced apart from the cathode plate 10 and the anode plate 20 by a predetermined gap.
The mesh grid 40 has a fixing hole 41 through which the spacer 30 passes and an electron beam-controlling hole 42 which corresponds to the gate hole 15a. A binder 43 is filled in the fixing hole 41 so that the mesh grid 40 is coupled to the spacer 30.
A method for coupling a spacer in a conventional field emission device having the above structure will be described as below.
First, after the phosphor layer 23 is formed on the anode electrode 22, the spacer 30 is disposed in the anode plate 20 at a predetermined interval in a state when the phosphor layer 23 has not been fired yet and then is fixed using a binder in a paste state. Next, the spacer 30, fixed in the anode plate 20, is inserted in the fixing hole 41 of the mesh grid 40 manufactured from a metallic plate, and then, the binder 43 for fixing the spacer 30 is filled in the fixing hole 41.
The mesh grid 40 and the spacer 30 are aligned, the binder 43 is cured, and then, the phosphor layer 23 is fired. The anode plate 20 and the cathode plate 10 are aligned with each other, and vacuum packaging is performed.
In the aforementioned conventional method, when a binder is cured at a temperature of about 120° C. and a phosphor layer is fired at a temperature of about 420° C., a mesh grid may be deformed by a high temperature heat and may be not well aligned with an anode plate. In particular, during vacuum packaging, secondary deformation of the mesh grid and upset of alignment of the mesh grid with the anode plate occur at a process temperature of about 300° C. or more. FIG. 1B is a photo showing a screen of the conventional field emission device, and it can be know from FIG. 1B that an image is not uniform and smeared by a deformed mesh grid.
Due to the deformation and scattering of the mesh grid and generation of the stray electros, which may cause lowering of picture quality, the performance of the field emission device is deteriorated and thus, a new method for solving these problems is required.